title: Theoretical and experimental studies of hydrogen adsorption and desorption on Ir surfaces.
abstract: We report adsorption and desorption of hydrogen on planar Ir(210) and faceted Ir(210), consisting of nanoscale {311} and (110) facets, by means of temperature programmed desorption (TPD) and density functional theory (DFT) in combination with the ab initio atomistic thermodynamics approach. TPD spectra show that only one H2 peak is seen from planar Ir(210) at all coverages whereas a single H2 peak is observed at around 440 K (F1) at fractional monolayer (ML) coverage and an additional H2 peak appears at around 360 K (F2) at 1 ML coverage on faceted Ir(210), implying structure sensitivity in recombination and desorption of hydrogen on faceted Ir(210) versus planar Ir(210), but no evidence is found for size effects in recombination and desorption of hydrogen on faceted Ir(210) for average facet sizes of 5-14 nm. Calculations indicate that H prefers to bind at the two-fold short-bridge sites of the Ir surfaces. In addition, we studied the stability of the Ir surfaces in the presence of hydrogen at different H coverages through surface free energy plots as a function of the chemical potential, which is also converted to a temperature scale. Moreover, the calculations revealed the origin of the two TPD peaks of H2 from faceted Ir(210): F1 from desorption of H2 on {311} facets while F2 from desorption of H2 on (110) facets.
authors.affiliation: Institute of Electrochemistry, Ulm University, Ulm, Germany. payam.kaghazchi@uni-ulm.de
authors.forename: Payam
authors.initials: P
authors.lastname: Kaghazchi
authors.forename: Timo
authors.initials: T
authors.lastname: Jacob
authors.forename: Wenhua
authors.initials: W
authors.lastname: Chen
authors.forename: Robert A
authors.initials: RA
authors.lastname: Bartynski
mesh_terms: D000327:Adsorption; D006859:Hydrogen / Q000737:chemistry*; D007495:Iridium / Q000737:chemistry*; D011789:Quantum Theory; D013499:Surface Properties
chemical_list: D007495:Iridium; D006859:Hydrogen